The present invention relates to UV curable controlled release coating compositions utilizing an epoxy silicone fluid, a cationically polymerizable styrene compound, such as .alpha.-methyl styrene or a derivative thereof or a p-substituted styrene compound, and a photoactive aromatic onium salt, such as a diaryliodonium hexafluorometalloid salt.
Prior to the present invention, silicone release coatings were widely used to render various surfaces non-adherent. Non-adherent silicone treated paper is often used to support labels contacting a pressure-sensitive adhesive (PSA) prior to the use of such labels. In addition, non-adherent surfaces are often necessary in industrial packaging.
Silicones have been widely recognized for their value as release coatings particularly with respect to their use with PSAs. The release coating industry is also searching for ways to synthesize release coating compositions which can be converted to cured release coatings having a predictable variation in release characteristics when contacted with PSAs, referred to hereinafter as "controlled or differential release".
Certain coating compositions utilizing epoxy or acrylic functional groups as modifiers of the release properties of cured silicone resins are taught by U.S. Pat. No. 4,576,999. UV cured epoxysilicone polymers having controlled release also are discussed in copending application Ser. No. 171,498, filed Mar. 21, 1988, utilizing condensed organosiloxy units substituted with esterified benzoyl groups. Another method for modifying release characteristics of UV curable epoxy functional silicones is taught in U.S. Pat. No. 4,547,431, resulting from the addition of epoxy monomers.
Controlled or differential release of organopolysiloxane resins is also discussed in copending application Ser. No. 225,986, filed July 29, 1988. Organopolysiloxanes are modified with monovalent phenolic radicals having from 6 to 26 carbon atoms, monovalent acrylic organic radicals, or monovalent epoxy functional organic radicals. These modified silicones have been found to have controlled release The incorporation of the phenolic groups onto the organopolysiloxane backbone is achieved by an SiH to vinyl addition reaction catalyzed by a platinum catalyst. Although effective controlled release results are achieved, it has been found that residual amounts of unreacted allylphenol used to incorporate phenolic groups into the resin, often impart an undesirable phenolic odor to the silicone release resin.
Improved substantially odor free UV curable compositions are shown in copending application Ser. No. 07/369,900. Although various UV curable epoxy silicone compositions have been provided, significant effort is being expended by the silicone industry to find additional silicone release coating compositions capable of providing silicone coatings with controlled release characteristics.